Hi David, On 2018-11-26 at 17:36 +1000, David Holmes wrote: > Hi Jakub, > > On 26/11/2018 1:53 am, Jakub Vaněk wrote: > > Hi, > > > > This patch raises the minimum architectural level for ARM CPUs to > > ARMv5TE. It is done through changing the -march flag in the current > > CPU-specific CFLAGS and ASFLAGS. > > > > This patch depends on "Append assembler flags on ARM targets" patch > > for > > ASFLAGS handling. > > > > Reason for this change: assembler code in linux_arm_32.s uses PLD > > instructions. ARM ISA manual mentions this: "This instruction is > > available in E variants of ARM architecture v5 and above." (thanks > > to > > David Holmes for noticing this). > > FYI I did a bit of digging and we tried to make this change back in > 2010 > and ran into problems: > > "It appears that gcc assumes that if you choose the armv5te > architecture > option, it can use the "E" instruction extensions which provide 64 > bit > load and stores to 4 byte aligned addresses. I tried two different > compiler versions 4.1.2 and 4.2.3 and they both had the same > problem. > The <hardware> does support ldrd/strd but they do not support 4 byte > aligned operations. The addresses must be 8 byte aligned."
> How things stand today I can not say. I have searched for this and indeed, this bug wasn't fixed until recently: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82445 For our own use, it seems that Ubuntu gcc7 is patched, whether Debian gcc6 isn't. I think that the best solution is to keep armv5t in CFLAGS and only raise armv5te in ASFLAGS, where it is actually needed. This way GCC still generates older non-buggy code and the assembler works with pld. I have tested this configuration and it compiles successfully. https://ci.adoptopenjdk.net/view/ev3dev/job/openjdk12_build_ev3_linux/40/ Thanks, Jakub > > Cheers, > David # HG changeset patch # User Jakub Vaněk <[email protected]> # Date 1543252130 -3600 # Mon Nov 26 18:08:50 2018 +0100 # Node ID bfd9e7032cfdc8c814ddaf4bb471a014fbbf1a89 # Parent d2db3b32d5614029f2b1af2731c0d9ec10d88767 Fix undefined pld instruction on arm-sflt diff --git a/make/autoconf/flags.m4 b/make/autoconf/flags.m4 --- a/make/autoconf/flags.m4 +++ b/make/autoconf/flags.m4 @@ -46,6 +46,11 @@ AC_MSG_CHECKING([for ABI profle]) AC_MSG_RESULT([$OPENJDK_TARGET_ABI_PROFILE]) + # --- Arm-sflt CFLAGS and ASFLAGS --- + # Armv5te is required for assembler, because pld insn used in arm32 hotspot is only in v5E and above. + # However, there is also a GCC bug which generates unaligned strd/ldrd instructions on armv5te: + # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82445, and it was fixed only quite recently. + # The resulting compromise is to enable v5TE for assembler and let GCC generate code for v5T. if test "x$OPENJDK_TARGET_ABI_PROFILE" = xarm-vfp-sflt; then ARM_FLOAT_TYPE=vfp-sflt ARM_ARCH_TYPE_FLAGS='-march=armv7-a -mthumb' @@ -57,11 +62,11 @@ elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarm-sflt; then ARM_FLOAT_TYPE=sflt ARM_ARCH_TYPE_FLAGS='-march=armv5t -marm' - ARM_ARCH_TYPE_ASFLAGS='-march=armv5t' + ARM_ARCH_TYPE_ASFLAGS='-march=armv5te' elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarmv5-vfp-sflt; then ARM_FLOAT_TYPE=vfp-sflt ARM_ARCH_TYPE_FLAGS='-march=armv5t -marm' - ARM_ARCH_TYPE_ASFLAGS='-march=armv5t' + ARM_ARCH_TYPE_ASFLAGS='-march=armv5te' elif test "x$OPENJDK_TARGET_ABI_PROFILE" = xarmv6-vfp-hflt; then ARM_FLOAT_TYPE=vfp-hflt ARM_ARCH_TYPE_FLAGS='-march=armv6 -marm'
